Polymer industry has been playing a pivotal role in the petrochemical industry, and production processes for polymers have undergone various kinds of technological innovation in correspondence with trends in the polymer industry.
The production processes for polymers are classified into a batch type process and a continuous process in terms of a system, and are classified into, for example, a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and a vapor phase polymerization method in terms of the form of a reaction system. In addition, a general process includes polymerizing a monomer with a polymerization catalyst to provide a polymer.
In association with the progress of a polymerization process, a reduction in production cost, resource savings and energy savings have started to become important challenges in process development. Important technological innovation in the reduction in production cost has heretofore been performed by dramatically increasing the amount of production of a polymer per hour through the development of a high-activity catalyst. For example, switchover to a non-deashing process or vapor phase process in the production of polyethylene or polypropylene can be said to be an example of the innovation. The recovery of a polymerization catalyst, an unreacted monomer, and a polymerization solvent after a polymerization reaction, thereby being recycled and re-used, is also effective in the reduction in production cost. JP 2000-063405 A (Patent Document 1) describes the following production method. In the slurry polymerization for producing polyethylene, a polymer is subjected to solid-liquid separation from a polymerization reaction liquid, and then the resultant recovered liquid is returned to a polymerization step, followed by recycling and re-use. It is difficult to separate and recover a high-activity titanium-based catalyst used as a polymerization catalyst while maintaining its catalytic activity, and the recycling and re-use of the recovered liquid are intended for its utilization as a polymerization solvent.
Meanwhile, the following attempt has been made in the polymerization of α-olefin such as ethylene or propylene. A polar group-containing monomer is copolymerized with olefin to impart various functions such as dyeability, adhesive property, and compatibility with engineering plastic to nonpolar polyethylene or polypropylene.
There have been known examples proposed by Brookhalt (J. Am. Chem. Soc., 118, 267 (1996); Non-Patent Document 1), Nozaki (J. Am. Chem. Soc., 131, 14606 (2009); Non-Patent Document 2), et al. in each of which a catalyst made of a complex of a metal in Group 10 of the periodic table is used as a polymerization catalyst capable of copolymerizing olefin and a polar group-containing monomer. However, those complex catalysts have involved the following problem. The polymerization activity of each of the catalysts is low in spite of the fact that a precious late transition metal is used, and hence a ratio of a catalyst cost to a production cost is high in a conventional polymerization process, which is not economically commensurate.